The present invention relates to thermoelectric materials, and more particularly, thermoelectric materials including a filled skutterudite structure.
Thermoelectric materials are a class of materials that efficiently convert thermal energy to electrical energy or convert electrical energy into thermal energy. The “Seebeck effect” is the phenomenon underlying the conversion of thermal energy into electrical energy, while the “Peltier effect” is the phenomenon underlying the conversion of electrical energy into thermal energy. In power generation applications, for example, thermoelectric materials typically include free electrons or free electron holes that create an internal electric field in the presence of a temperature gradient. The internal electric field results in a buildup of voltage between two electrodes to provide a source of electrical power.
The performance of thermoelectric materials is generally characterized by a dimensionless figure of merit, ZT=σS2T/κ, where σ is the electrical conductivity, S is the Seebeck coefficient, T is the temperature, and κ is the thermal conductivity. The larger the value of ZT, the higher the efficiency of the thermoelectric material. An efficient thermoelectric material should therefore possess a high electrical conductivity, a large Seebeck coefficient, and a low thermal conductivity. While there are no known upper limits to the value of ZT, in practice materials having a value of ZT greater than one are rare.
Filled skutterudites represent a class of artificially or naturally structured thermoelectric materials having good electrical conductivity, modest to high Seebeck coefficients, and low thermal conductivity. Filled skutterudites are structurally related to the mineral skutterudite, CoAs3, but contain guest atoms in the interstitial voids in its crystalline structure. One such category of filled skutterudites, rare earth filled skutterudite, is represented by the formula RxT4Sb12, where R is a rare earth element, x is a guest fraction, and T is Iron (Fe), Cobalt (Co), or a mixture of these elements. Rare earth filled skutterudites have been shown to exhibit a lower thermal conductivity, κ, and thus a higher figure of merit, ZT, when compared to unfilled skutterudites and other thermoelectric materials. As a result, rare earth filled skutterudites have been proposed as a thermoelectric material for thermoelectric power generators, solid state thermoelectric coolers, and solid state thermoelectric heaters.
Despite the advantages of rare earth filled skutterudites, the relatively high cost of component materials contributes to their overall high cost. Therefore, there remains a need for an improved, low-cost filled skutterudite suitable across a wide range of thermoelectric applications.